A novel pathogenic variant p.Asp797Val in IFIH1 in a Japanese boy with overlapping Singleton-Merten syndrome and Aicardi-Goutières syndrome.

Pathogenic-activating variants of interferon induced with Helicase C domain 1 (IFIH1) cause Singleton-Merten (S-M) syndrome, which accompanies acro-osteolysis, loss of permanent teeth, and aortic calcification, as well as causing Aicardi-Goutieres (A-G) syndrome, which shows progressive encephalopathy, spastic paraplegia, and calcification of basal ganglia. Recently, patients with overlapping syndromes presenting with features of S-M syndrome and A-G syndrome were reported. However, progression of clinical features of this condition has not been fully understood. We report a Japanese boy with a novel pathogenic IFIH1 variant who presented with clinical features of S-M syndrome and A-G syndrome.